The present invention relates to a voltage measuring device which detects a voltage of a multiple-set battery including plural unit cells connected in series to output a desired voltage.
For example, electric vehicles or hybrid vehicles include a high-voltage battery as a motor driving power source. Such a high-voltage battery obtains a high voltage by connecting plural unit cells in series, which are secondary batteries (storage battery) such as a nickel-hydrogen battery or a lithium battery.
All the secondary batteries are charged or discharged with the same power. Accordingly, when the secondary batteries have different deterioration conditions, the secondary batteries tend to be easily overcharged or over-discharged. Therefore, not to be overcharged or over-discharged, it is necessary to check the charging conditions of the unit cells. Accordingly, plural unit cells (for example, 55 unit cells) are partitioned into, for example, five blocks (that is, one block includes 11 unit cells), and the voltage of each block is measured in real time by a voltage detecting IC disposed every block.
The decrease in residual capacity of such secondary batteries can make it difficult a vehicle to travel any more, and thus it is necessary to avoid the waste of power. Accordingly, for example, a technique described in JP-A-2009-17657 has been proposed. In JP-A-2009-17657, the waste of power of the secondary batteries is prevented by switching the power supplied from the secondary batteries to a low-power consumption mode.
However, the above-mentioned voltage measuring device is switched to a low-power consumption state by turning off the voltage detecting IC when the voltage measuring device is out of order. Accordingly, when the voltage measuring device works normally and the voltage of the high-voltage battery does not vary, the low-power consumption operation is not performed. For example, it is assumed that the vehicle stops and the air conditioner is turned on. In this case, since the vehicle stops with its ignition turned on, the voltage of a high-voltage battery does not vary, but current is consumed to measure the voltage of the secondary battery. Accordingly, there is a problem that it is not possible to suppress power consumption with high precision.